The invention relates to a network comprising at least two lines and network users. Such networks are known in many forms and are used to transfer data between the network users.
For use in vehicles, several bus systems are also known. In the last few years, the CAN bus has become particularly known. It is especially used for transferring control information and for sensor detection. However, similarly as other known bus systems, this bus system is not capable of transferring both data and energy for the network users.
It is an object of the invention to provide a network which is equally suitable for both data and energy transfer and for which a minimal number of connection lines is sufficient.
According to the invention, this object is solved in that the two lines of the network are formed both for data transfer among the network users and for energy transfer from a voltage source to the network users, in that the data are symmetrically and differentially transferred through the two lines, in that a terminal of the voltage source is coupled to the two lines, in that the network users are coupled to the other terminal of the voltage source via a different electric connection separated from the network, in that the network users symmetrically couple out the energy transfer via the two lines of the network, and in that the two lines are mutually insulated.
The network thus comprises two lines which are formed both for data transfer among the network users and for energy transfer to the network users. A terminal of a voltage source is coupled to the network users via the two lines of the network. Another terminal is coupled to the network users via another path which does not belong to the network.
The data transfer takes place symmetrically and differentially through the two lines, i.e. a data bit is transferred with different polarities through the two lines.
However, the energy transfer is implemented in such a way that possibly equal currents flow in the two lines. This is achieved by a symmetrical coupling-out of the energy by the network users from the two lines of the network.
It is thereby achieved that the two lines are suitable for both energy and data transfer.
Due to the differential transfer of the data and the symmetrical transfer of the power supply currents on the two lines, it is achieved that disturbances in the power supply line have only a very weak effect on the data transfer so that the transfer of information is not affected under these circumstances.
As compared with known solutions, not only fewer lines but also fewer contact points are required. This enhances the reliability.
Since a terminal of the energy transfer is jointly transferred through the two lines of the network, energy transfer is still guaranteed in the case of a drop-out of a line or the connection of such a line to a network user. Only the data transfer is then disturbed; the network user can, however, continue to work, for example, with an emergency program. This is of great importance, particularly in vehicles. By transferring a pole of the energy transfer jointly via the two lines of the network, the cross-section of the individual lines can be halved as compared with the original power supply line so that the signal transfer does not require substantially any additional line cross-section.
There should be a good magnetic and capacitive coupling between the two lines of the network. This may be achieved, for example, by twisting the lines. Due to the satisfactory coupling which is thereby achieved between the two lines, ambient magnetic and electric alternating fields substantially have the effect of common mode disturbances on the two lines and thus do not disturb the data transfer, which takes place differentially.
An embodiment of the invention as defined in claim 2 provides advantageous embodiments, particularly for the network users. These can couple in and couple out the data inductively or capacitively. Since particularly a symmetrical coupling-out of its consumption current from the two lines of the network is important, inductances are provided in the network users, via which inductances these currents are coupled out. Simultaneously, these inductances mutually decouple the two lines, which is again necessary for the data transfer. In this relatively simple way, both a decoupling of the two lines and a symmetrical coupling-out of the consumption currents can thus be achieved.
As is provided by a further embodiment of the invention as defined in claim 3, the differential evaluation of the data transferred through the two lines of the network can be advantageously realized by means of a differential amplifier.
Coupling-in can again be effected advantageously, as defined in claim 4, by means of an amplifier which has a non-inverting and an inverting output which are each coupled to one of the two lines of the network.
In a further embodiment of the invention as defined in claim 5, the network should be basically arranged in a star configuration. Ring-shaped wiring within the network may cause low-frequency currents. To avoid them, it is advantageous to provide a ring coupler which DC separates the lines within such a circuit. A short-circuit of low-frequency currents in such a ring is thereby prevented. A magnetic and capacitive coupling between the two lines of the network which is advantageous for the function of the network, as defined in claim 6, may be achieved, for example, by twisting these lines.
As already described above, a terminal of the energy supply can be connected via the network. Another terminal is to be connected to the network users via a different path. For example, in vehicles, this may be the chassis. However, for given applications, it is possible, as defined in claim 8, to provide two networks according to the invention each taking over a terminal for the energy supply. In this case, the data can then be advantageously transferred redundantly through the two networks. This results in an additional reliability of transfer or security against failures.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.